Politics: Who wins US Election ?

From various debates between senator John McCain & Brack Steven Obama the GOP show that Mr. Obama is lading by 6 points including the popular votes in battle states.But do you believe that despite trailing in the gallop poll , Mr. McCain may win the US election 2008 to occupy the white house?
From the past elctions of 2000 & or before it was found while in the primaries, the leader who had been leading never won the battle in the White House.Like in the election of 2004, Mr. John Kerry was leading over President Bush by a greater margin . In the last day of the vote John was leading until mid night. Lastly what happened?
He conceded to Mr. Geroge W Bush.